Automatic line level regulation of multiple channel television systems



Dec. 15, 1936. Y J HERMAN 2 ,064,540

AUTOMATIC LINE LEVEL REGULATION OF MULTIPLE CHANNEL TELEVISION SYSTEMS Filed 001?. 11, 1932 INVENTOR J. HERMAN ATTORNEY Patented D c. is, 1936 UNITED} ST TES AUTOMATIC LINE LEVEL REGULATION or Y -MULTIPLE CHANNEL TELEVISION s s- 'TEMS Joseph Herman, Testthild, N. 3., assignor-to American Telephone and Telegraph Company.- a corporation of New Xork Application October 11, 1932, Serial No. 637,321

24 Claims.

This invention-relates to multiple channel signal transmission and more particularly to a method and means for equalizing the intensity of the signals in the various channels at the receiving station of a multiple channel electrooptical system.

An object of this invention is to provide apparatus for and methods of automatically causing the signal currents transmitted over the different channels of a multiple channel transmission system to have substantially equal intensities when impressed upon the translating device at the receiver, irrespective of different transmission variations in the several transmission channels.

Heretofore, manual means have been provided for adjustment of each of the transmission channels so as to cause the component parts of a received signal from each channel to uniformly affeet the receiving device and thus eliminate variations as between the different channels and also to hold the transmission level of each channel to a given level.

- In this system one of the channels is used as a reference channel and the variations in level of the other channels are automatically equalized therewith so that the efiective level of all channels is substantially the same although not necessarily of constant value.

In multiple channel television systems in which successive line series of elemental areas of a field of view are being scanned simultaneously and transmitted over different channels, it is necessary to keep the relative transmission levels ofthe different channels substantially constant. If this is not done the channel having a higher or lower transmission level gives to the received image a strongly lined appearance, which to a large extent offsets the higher resolving power obtained'from multiple channel operation. The arrangement disclosed herein overcomes this disadvantage by automatically adjusting the transmission level of the different channels at the receiving station and also at an intermediate repeating station if desired, so that the effective level will be substantially the same on all channels. For this purpose the transmission level of one of the channels averaged over a small period such as a complete scanning cycle is taken 'as the reference level and the other channels are adjusted to substantially the same level. This is automatically done continuously and rapidly from' channel to channel while the signals are being received. The operation of the system is conditioned uponeach channel transmitting signal current generated at the transmitting station by thescanning of at least a part of the elemental areas distributed throughout the field of view or by different channels and in systems where wider strips comprising a plurality of elemental strips are scanned by the different channels if a rotation of the scanning occurs as between the different wide strips and the difierent channels so that each channel repeatedly scans substantially the entire field.

. In the arrangement shownv for illustrating a method and means for carrying out this invention,

' the automatic level regulator is applied at the receiving station to a three channel electro-optical system. The three incoming transmission channels are connected to the input sides of three push-pull amplifiers, respectively, the output sides of which "are connected to the three channels of a multiple electrode receiving neon tube or three separate light sources. The receiving light translating device is associated with suitable multiple channel scanning means for producing the image, the scanning means shown consisting of a scanning disc in which the apertures are provided with suitable optical prisms so that the light from the three electrodes of the light source is properly deflected and distributed in constructing the image. A suitable multiple channel scanning arrangement of this kind is disclosed in the patent of Herbert E. Ives, 1,989,618, dated January 29, 1935. Another suitable arrangement is disclosed in the copending application of O. B. Blackwell and J. Herman, Serial No. 393,568 filed September 18, 1929.

A more detailed description of the invention follows and is illustrated in the accompanying drawing:

Figure 1 is a schematic representation of the receiving apparatus of a multiple channel television system arranged for automatically equalizing the intensity or the signals in the several channels; and

Fig. 2 is a sectional view of a portion of the scanning disc through an aperture thereof.

Fig. 1 shows the transmission level regulator television system. The level regulating appara-.

asappliedtothenceivingendciathreechannel tile is applicable to other systems than television equippedwith vacuum tubes having variable ,i

systemsandmayalsobeappliedatan intermediate repeating station. when applied at an intermediate point it, of course, only equaliaesfor variations up to that point and ii appreciable level occur beyond the regulator. it may also be applied at the receiving station.

Thethreeincoming on channels ll, 2|and||areconnectedtotheinputsidesotthree pmh-pull amplifiers Ii, ii and ll, respectively,

I characteristic or arrangements for controlling the gain or the amplifiers in small steps by electrical V or electromagnetic means. The output sides .0: these amplifiers are connected to the three channels oi the television receiving lamp I" of the television receiver i||'. Separate light sources, oneioreachchannel mightbeusedinplaceoithe multiple electrode light'souroe I. The receiving lamp as shown consists of three electrodes Ill. Ill'and Ill connecting respectively with one terminal o! the output side oi the-amplifiers associated with channels l|, 2| and and a common electrode I connecting in common with the .server positioning plate A scanning disc "I- associated with lens system Ill-2|! and driven by motor III contains a set of spirally arranged apertures, each aperture of which is equipped with a prism or the equivalent for directing light through its associated aperture from one ofthe light As many prism equipped apertures as there are multiple channels operating si-.

multaneously pass the viewing field and simultaneously direct light from each of the difierent channels into the eye 01 the observer. In a threechannel system as'shownin the drawing the angle of each prism in such that one-third oi the prisms direct the light into the eye from each of the three channels, respectively, during a scanningcycle. For example, apertures I, 2 and 3 of the spiral may direct light from channels ll, 2| and 3|, respectively; apertures l, S and of the spiral also may direct light from channels ll, 2| and respectively, andso on. The scanning operation at a receiving station is, of course, performed in synchronism with a similar scanning operation at a transmitting station. Such a scanning arrangement for both ton and reception is disclosed in the patent of Herbert E. Ives, No. 1,989,818, dated January 29, 1935, supra.

Fig. 2 shows asection of a portion of scanning disc Ill and a light deflecting prism 2|! associ-' ated with. a scanning apertm'e.- The lens I" collects light from the light sources of all channels Band directs it to the field of view while each of the prisms transmits through its associated apei'ture the light which comes onlyirom the light source of one channel. This is brought about by designing each prism to give the proper degree of deflection to associate its aperture with the light source or a given channel.

Reierringagaintol'ig. Lchannelllisusedas a reference channel. It is provided with an amplifier havingthe usual negative grid battery 32. Channels II and 1| have condensers l2 and 22 amu connectedinthegridcircuitsottheiramplifiers.

insteadoi grid batteries in order to permit of gain adjustments by the impressing 01' different values or nu'ative voltage on these condensers.

An auxiliary amplifier 4 I which is connected permanently across the output or amplifier}! is also provided with a condenser llior gain adjustment. The charging and discharging circuits of these condensers are provided with resistance II, II and litolimittherate oicharsing anddischarging. A

The level regulating device consists,- of two circuit networks comprising two detectors or 'rectifiers 1| and 8|, two low-pass filters N and Ill, and a difierential voltmeter relay Ill. A

rent strength in channel 3| is continuously obtained from rectifier 1| whose input is connected to the output of amplifier 4| through the transformer II and the adjustable potentiometer ll.

rectified current depending upon the signal cura second rectified current depending upon the current strength in each of the several channels, respectively, is obtained from rectifier 8| whose input is connected to the brush arm lot the distributor l|| which, through transformer N and the regulating potentiometer It, connects it in turn with channels l|, 2| and respectively, for. a time interval which may conveniently be a multiple oi the picture scanning period of 15 to /20 of a second. I! the time interval is made too short, the samples or received current taken from channels III and 2| for comparison with the current of channel 3| may not be of sufilclent duration to show the average intensity of the signals on these channels. This is because the relative intensity of the currents on thevarious channels may difier greatly during a short period oi time since they are produced by the scanning of slightly diiIerent-portions oi the field or view which may have a large degree of contrast. Only by taking samples corresponding to a fairly large part otthe field of view or to one or more complete scannings oi the field of view and averaging or smoothing out the variations in rectified current derived from each channel, can the relative intensity oi' the signals received over the different channels be accurately determined. The lowpass filters l0 and l|| are used for the purpose of smoothing out the rapid variations in the rectified television currents. The band width 01' these filters is dependent uponthe length of the time interval allowed for each sample of current The shorter the time interval the greater the band width which must be used. For time intervals corresponding to several complete scannings, the filter need pass only the frequencies up to about 15 cycles or less. The current at the output of filter III is a smooth but continuous envelope or theaverage rectified current of the successive samples taken from the various channels by means of the distributor "I, while the current at the output 01' filter ll is an equally smooth and continuous envelope of the average rectified current derived from the reference channel. These envelopes of current are applied differentially to the voltmeter relay Ill and move its armature to one or the other of its contacts whenever one or the other of the two currents predominates.

A source oi space current- IN is connected to rectifier 1| through resistance I H and low-pass filter 9|, and to rectifier through resistance Ill and low-pass filter l.||. When the output currents of rectifiers II and III are equal, balancing opposing currents flow through similar resistances ill and 2, respectively, and there is no.

the relay armature I22 is drawn against contact unbalanced voltage drop between the exterior terminals or theseresistances towhich the .Winding I2I oi the voltmeter relay I24 is connected.

Consequently the armature; I22 the relay I24,

under these conditions-remains in its neutral position with its contact arm midway between adjustable contacts I22 and I24, but if the output currents of rectifiersltand 20 are unequal a voltage drop occurs between the exterior terminalsoi'the resistances. III and III and a current flows in winding III of relay I24 causing its armature II2 to move its contact arm to engage one or the other of contacts I22 or I24 depending upon whether the outputcurrent from rectifier or Cl is the larger. The rectified curre'ntin the output or rectifier Iii dependsupon the current strength of the particular channel to which it happens to be connected. by the distributor I30, while the rectified current in the output 01' rectifier 10 depends upon the current strength in thereference channel 34. The contact arm of armature I22 oi the regulating relay, which may connect with either the negative battery I24 or ground I24 or take a neutral position, is connected to brush arm I of distributor I40 which rotates in synchronism with brush arm "I or distributor I38. The segments of distributor I42 connect the contact arm of relay armature I22 to the various condensers I2, 22 and 42 {or gain adjustment purposes. Attenuators I4, 24 and 34 are connected in series with'each of the output circuits from the different channel amplifiers and attenuator 44 is connected in the input circuit of amplifier 4|, the purpose of which will be described later.

A feature of the level regulating deviceis its automatic and continuous action both to control the relative levels 01 the signals and also to remove any differences in sensitivity between the two sides or networks of the regulating apparatus. v

The operation of the arrangement isas follows:

Both branches or networks of the regulatingdevice should be free of any unbalance andthis condition may be obtained. by connecting both branches to the same source of current. This occurs when the brush arms l8! and I" are in contact with segments lv of distributors I 30 and I40, respectively.. In this position both branches of the regulating device are connected in parallel to the same sourceoi signal current,

namely, that on channel 30; A local source of current might be used for this purpose by using suitable obvious connecting means to properly connect and disconnect this source. If the rogu lating apparatus .is unbalanced the contact arm oi the relay armature I22 will be moved against one or the other of contacts I23 or I24. This will either increase or decrease the charge on the biasing condenser 42 and thus vary the gain of ampli fier 4| until the current passing through the two branches of the regulating apparatus is balanced.

If the larger current is flowing through the branch containing rectifier III the contact arm,

of the relay armature I22 will be drawn against contaot, l24, thus connecting the-condsenser 42 with the biasing battery I25 which results in reducing the gain of this branch until the current passing through it is equal to that of the other branch and the relay armature I22assumes a neutral position with its contact arm between the contacts I22 and I24. If the current flowing through the branch of the regulating device-containing rectifier III is larger than that flowing through the other branch the contact arm of am I3I and MI.

I22 and the condenser 42 is then connected to and make contact with the other segments of their respective distributors," the average level channels I0 and is balanced against the- As these brush arms rotateaverage level or channel III. when rectifier 4! .is connected to the; output of amplifier II or channel It through segment I or distributor in and the contact arm of the regulating relay connected to condenser I2 through-segment I or distributor .I4ll this-condenser will be. charged or discharged depending upon 'the'position or the relay armature I22. If the strength of the signal currents, as smoothed out by the low-pass filters 90 and I00 in the regulating circuits is greater in channel I0 than in channel at the relay, at will connect the negative battery I to condenser I2 thereby reducing the gain of the ampliile'r II of channel;III. f the current strength in channel III is smaller than in channel 20 the relay will connect ground to condenser I2 thereby. reducing its charge and increasing the gain of amplifier II. A similar operation takes place on amplifier 2I.oi channel 20 whendistributor. I

through segment 2 connects rectifier iii] to channel 20, thus adjusting the gain of amplifier 2I. As the brush arms continue to rotate they next connect both branches of the regulating device in.

not to regulate the transmission level of channel 30 .but to compensate for any imbalance in the regulating apparatus as already described. Thissystem permits ordinary transmission level variations in the reference channel to occur and its regulating action is primarily to automatically adjust the other channels to'cause the, average current in each to be substantially equal to that in-the reference channel.

Since the maintenance ofsubstantlally equal levels at the outputs of different channel amplifiers does not insure equalbrilliancy in the light emitting elements of the light source 209 in the receiver 280, attenuators I4, 24 and 34 are connected in series with each of the output circuits from the amplifier to permit adjusting the input currents to the light translating device so as to produce equal 'brilllancy from equal signal currents. This adjustment, however; need be made only when setting up the apparatus or when replacing thelightv translating device or the like. An additional attenuator 44 is connected in the input of amplifier H for the pu pose of partly oil-setting and adjusting the gain introduced by this amplifier into the circuit of, rectifier III.

While the level regulating arrangement which has been described above has been shown as applied to a three channel television system, it is obvious that it can be readily applied to a system having a much larger number of channels. It is also obvious that such transmission level equalizing arrangements are not limited to television systems but are applicable to other communication systems, in whichthe average energies or currents transmitted into various channels at the receiving station, are approximately equal.

-Examples oi such systems are multi-channel twotone carrier telegraph, multi-channel and carrier or radio telephone'systems in which the carrier current is transmitted.

It will alsobe obvious that the regulating apparatus may be caused to function in such a manher that instead of maintaining equal'relative transmission levels at the output of the amplifiers H, 2! and Ii, it will maintain predetermined difierences in the relative levels. This can be accomplished by connecting attenuators in series with the leads .from the output of amplifiers II,

II and SI, tothe segments I, 2 and I of distribue tor ill.- If an attenuator having'a certain loss is connected in series with the lead to segment I,

the output of amplifier II will be adjusted to a level which is higher than that of amplifier ll by the loss in the attenuator. Similarly.- an attenuator in series with the lead to segment 2 will increase the output level of amplifier II with re-- spect to that of Si by the amountof loss in the attenuator. An attenuator in series with the lead to segment 3 will however cause a lower level at the output of amplifiers II and 2| with respect to that of ii by the loss introduced by the attenuator. A similar result is of courselaccomplished by considering the output of the amplifiers to include the attenuators ll, 24 and 34 and adjusting these attenuators to obtain the desired differences in level.

While the invention in its narrower aspects pertains to the automatic adjustment of the transmission levels of the channels of -a multiple channel television. system, certain features of the invention may obviouslyfind other uses. The various features or aspects of the invention are defined in the following claims.

What is claimed is:

1. The method of operating a multi-channel signaling system which comprises simultaneously cooperatively utilizing signaling currents received in two of said channels at a receiving station of said system to automatically change the transmission level characteristic of at least one of said channels.

2. The method of operating a multi-channel signaling system which comprises simultaneously cooperatively utilizing current received in two of said channels at a receiving station of said system both to reproduce the signal and to automatically change the transmission level characteristic of at least one of said channels.

3. The method of operating a multi-channel signaling system which comprises cooperatively utilizing energy transmitted over the several channels to reproduce the signal, permitting the transmission level of one of said channels to vary with changes in the transmission characteristics thereof and automatically adjusting the transmission level of the other channel or channels to maintain substantially constant the relative transmission level or levels with respect to that of said first mentioned one channel.

4. The methodof operating a multi-channel signaling system which comprises cooperatively utilizing energy transmitted over the several channels to reproduce the signal, permitting the transmission level of one of said channels to vary with changes in the transmission characteristics thereof and automatically and periodically adlusting the transmission level of the other channel or channels to substantially that of said first mentioned channel.

was

1 5. The method of operating a multi-channel image producing system whichcomprises cooperatively utilizing jimage currents. transmitted overa plurality of'channels of said system. to producean image, permitting the transmission level of one of said channels to vary with the transmission characteristicsoi said channel and automatically and periodically adJusting, the transmission level oi the remaining channel or channels to correspond to that of said first mentioned channel.

i 6. The method of operating a multi-channel television system which comprises simultaneously cooperatively utilizing current received in two of said channels at a receiving station'of said. system both to reproduce the image and to automatical-.

vutilizing current received in two of said channels "at a receiving station of said system to eifect an adjustment to restore a desired relationship between said currents with respect to an amplitude characteristic thereof whenever changes in transmission characteristics of said system have caused a change in'said relationship.

-8. A multi-channel television system compris-' ing means for receiving, signal energy representative of the light tone values of individual elemental areas or a field, means for simultaneously utilizing said signal energy received over the difierent channels to control the production of an image and means for automatically and simultaneously cooperatively utilizing a portion of said signal energy received over a plurality of said channels respectively to adjust the transmission level of at least one of said channels.

9. In a multiple channel signaling system, means for periodically averaging energy transmitted by each of the difierent channels for definite equal periods of time, and means for automatically 'and periodically adjusting the average output energy of one of said channels to substantially that of the average output energy of another channel under control of said average energy in said other channel.

10. In a multiple channel signal receiving system, regulating means forvsuccessively adjustingthe energy level of the diilferent channels to that of one of said channels, the said regulating means including two electrical networks for comparing energy levels and means for periodically balancing the sensitivity of the two networks.

11. A television system comprising receiving means at a receiving station for receiving signaling energy representative of the light tone values of individual elemental areas of a field and for utilizing it to repeatedly set up complete images of an object field each within the period of the persistence of vision, means for averaging over an entire field scanning period signaling energy derived from the received signal and having the same wave form, and means for utilizing said averaged energy to control a transmission characteristic of said system.

12. A multi-channel television receiving system comprising an amplifier'in each channel, a pair of comparison circuits, means for continuously associating the output of one of said amplifiers with one of said comparison circuits, distributing means for periodically associating in succession the output circuits of the other of saidamplifiers with the other of said comparison circuits, and means under control of said comparison circuits for maintaining fixed relationships between the output currents of said last mentioned amplifiers and that of the remaining amplifier.

13. In a multiple channel signaling system comprising a plurality of transmission channels each of which may vary independently of the others to vary its transmission characteristic, means for simultaneously utilizing the signal energy received over the diiIerent channels to produce an image, means for rectifying and averaging the signal current transmitted over each of the several channels, means constituting one of said channels a reference channel including means for controlling and automatically adjusting the transmission level of each of the other channels under control of the current of changing level in the said reference channel and in accordance with the level of said current so that the relationship between the levels in all channels remains substantially constant whatever their values may be.

14. In a multiple channel signaling system comprising a plurality of transmission channels eachot which may vary independently of the others to vary its transmission characteristic, means for simultaneously utilizing the signal energy received over different channels to produce an image, means for amplifying the signal received over each of said channels, means Ior adjusting the gain or the said amplifying means in all but one of said channels to maintain the transmission level of. each of the said channels substantially equal to that of the said one channel as the latter changes, and means controlled by incoming signal energy for controlling said adjusting means.

15. In a multiple channel signaling system comprising a plurality of transmission channels and means for simultaneously utilizing the signal energy received over the diflerent channels to produce an image, means for successively averaging for a definite period of time a portion of the energy transmitted over each 01' said channels except one 01' said channels which is used as a reference channel, means for continuously averaging a portion of the energy transmitted over said reference channel, means for periodically equalizing said averaged energy received over each of said channels except the said reference channel to substantially that of the average energy received over the said reference channel.

16. An image transmission system comprising two transmission channels for transmitting image'currents which during a scanning cycle or a substantial part thereof are respectively representative of different elemental areas oi the object field but have substantially the same average amplitude whenever said channels have the same attenuation characteristic, image producing means at a receiving station for utilizing the currents from said channels to produce an image, means for producing a voltage proportional to the current in one of said channels averaged over a substantial portion of a scanning cycle, means for producing a voltage proportional to the current in the other of said channels averaged over the same period, and means for simultaneously utilizing said voltages to automatically adjust the attenuation characteristic of at least one of said channels to maintain a desired relationship between the attenuation characteristics of said channels.

1'7. The method of operating an image producing system which comprises averaging at a receiving station an image current over a period at least of the order of that required to completely scan the field of view and periodically effecting an adjustment of said system under control of said averaged current.

18. The combination with a repeating device of means for applying an image current to said repeating device, current averaging means upon which the output current from said repeating device is impressed to average the image current variations, and means under control of said current averaging device to periodically adjust the transmission characteristic of said repeating device.

19. The combination with current averaging means, of means for continuously applying an image current to said averaging means, a repeating device, a condenser associated with said device for controlling its operation, and means under control of the image current averaged by said averaging device for periodically adjusting the charge on said condenser.

20. The combination with means for repeatedly averaging a television current, produced as the result of repeatedly scanning the same field of view, over separated periods each of at least the order of a complete scanning period, a condenser, and means for periodically charging said condenser under control or said averaging means.

21. A television system comprising two current averaging means, means for simultaneously impressing different portions of the television current upon said averaging means respectively, and means under the joint control of said averaging means for controlling a transmission characteristic oi said system.

22. A television system comprising an amplifier at a receiving station, means for impressing a television current upon said amplifier representative of the tone values of elemental areas distributed throughout the field of view and produced during a period at least of the order of that of scanning the complete field of view, means associated with the output circuit of said amplifier i'or averaging said current, and means under control of said averaged current for pcriodically adjusting a transmission characteristic of said system.

23. In a multi-channel signaling system, means for cooperatively utilizing signaling energy received at a receiving station in two channels of a multi-channel signaling system to automatically change the transmission level of one of said channels, comprising means for comparing the transmission levels of said channels, and means controlled thereby for adjusting the level of one of said channels. I

24. In a multi-channel signaling system, means for cooperatively utilizing signaling energy received at a receiving station in two channels oi a multi-channel signaling system to automatically change the transmissionlevel of one of said channels, comprising means for comparing the.

transmission levels of said channels, means controlled thereby for adjusting the level of one of said channels, and means for automatically adjusting a transmission characteristics! said comparing means.

JOSEPH 

